1. Field of the Invention
This invention is concerned with an improved process for converting synthesis gas, referred to as syngas, i.e., mixtures of gaseous carbon oxides with hydrogen or hydrogen donors, to form hydrocarbon mixtures. In one aspect, this invention is particularly concerned with a process for converting synthesis gas or syngas comprising carbon monoxide and hydrogen to hydrocarbon mixtures rich in aromatic hydrocarbons. In another aspect, this invention is concerned with a process for converting synthesis gas to hydrocarbon mixtures rich in C.sub.3 + hydrocarbons and particularly C.sub.5 + petroleum hydrocarbons. In still another aspect, this invention is concerned with providing novel catalyst composition for the conversion of synthesis gas to hydrocarbon mixtures.
2. Prior Art
Processes for the conversion of coal and other hydrocarbons such as natural gas to a gaseous mixture consisting essentially of hydrogen and carbon monoxide, or of hydrogen and carbon dioxide, or of hydrogen and carbon monoxide and carbon dioxide, are well known. Although various processes may be employed for the gasification, those of major importance depend either on the partial combustion of the fuel with an oxygen-containing gas or on the high temperature reaction of the fuel with steam, or on a combination of these two reactions. An excellent summary of the art of gas manufacture, including synthesis gas, from solid and liquid fuels, is given in Encyclopedia of Chemical Technology, Edited by Kirk-Othmer, Second Edition, Volume 10, pages 353-433, (1966), Interscience Publishers, New York, New York, the contents of which are herein incorporated by reference.
It is desirable to be able to effectively convert synthesis gas from any source such as from coal and natural gas, to highly valued hydrocarbons such as motor gasoline with high octane number, petrochemical feedstocks, liquefiable petroleum fuel gas, and aromatic hydrocarbons. It is well known that synthesis gas will undergo conversion to form reduction products of carbon monoxide, such as hydrocarbons, at from about 300.degree. F. to about 850.degree. F. under from about one to one thousand atmospheres pressure, over a fairly wide variety of catalysts. The Fischer-Tropsch process, for example, produces a range of liquid hydrocarbons, a portion of which have been used as low octane gasoline. The types of catalysts that have been studied for this and related processes include those based on metals or oxides of iron, cobalt, nickel, ruthenium, thorium, rhodium and osmium.
The wide range of catalysts and catalyst modifications disclosed in the art and an equally wide range of conversion conditions for the reduction of carbon monoxide by hydrogen provide considerable flexibility toward obtaining selected boiling-range products. Nonetheless, in spite of this flexibility, it has not proved possible to make such selection so as to produce liquid hydrocarbons in the gasoline boiling range which contain highly branched paraffins and substantial quantities of aromatic hydrocarbons, both of which are required for high quality gasoline, or to selectively produce aromatic hydrocarbons particularly rich in the benzene to xylenes range. A review of the status of this art is given in "Carbon Monoxide-Hydrogen Reactions", Encyclopedia of Chemical Technology, Edited by Kirk-Othmer, Second Edition, Volume 4, pp. 446-488, Interscience Publishers, New York, N.Y., the text of which is incorporated herein by reference.
In a book entitled "The Fischer-Tropsch and Related Synthesis" by Storch, Golumbic and Anderson, published by John Wiley and Sons, Inc., New York, it recites beginning page 309, "The use of ruthenium as a catalyst for the production of high melting wax from carbon monoxide and hydrogen was studied at the KWI for several years (1938-1941). The process is mostly of theoretical interest because of the high cost of ruthenium and the small commercial demand for the very high molecular weight paraffins produced by synthesis over ruthenium."
Further discussion of the investigation of ruthenium catalyst for the conversion of carbon monoxide and hydrogen is provided by H. Pichler in Advanced Catalysis, Vol. IV, 1952, beginning at page 289. Also an article published in I. & E.C. Product Research And Development, Vol. 4, No. 4, December 1955 beginning at page 265 by Karn, Schultz and Anderson entitled "Hydrogenation of Carbon Monoxide and Carbon Dioxide on Supported Ruthenium Catalysts At Moderate Pressure" emphasizes the unsuccessful results of the investigation for producing gasoline boiling range hydrocarbons. Only high molecular weight waxy materials were produced at pressures of 21.4 atmospheres and higher and methane was a primary product at 1 atmosphere pressure.
Recently it has been discovered that synthesis gas may be converted without intermediate formation of lower alcohols to higher hydrocarbons and particularly to C.sub.5 + gasoline boiling range hydrocarbon products by catalytic contact of carbon monoxide and hydrogen synthesis gas with a ruthenium containing catalyst in admixture with a special type of crystalline zeolite catalyst of particularly selective conversion characteristics.
It is an object of the present invention to provide an improved process for converting synthesis gas to hydrocarbon mixtures that contain large quantities of highly desirable C.sub.5 + carbon-hydrogen constituents. It is a further object of this invention to provide a ruthenium containing catalyst mixture suitable for converting a mixture of gaseous carbon oxides and hydrogen to a gasoline boiling range mixture of hydrocarbons. It is a further object of this invention to provide an improved method for converting synthesis gas under elevated pressure conditions to aromatic hydrocarbons. It is a further object of this invention to provide a method for converting synthesis gas to petrochemicals feedstocks, such as lower aromatics and olefins.